Light-emitting device and method for manufacturing light-emitting device

ABSTRACT

A light-emitting device including a window layer-cum-support substrate, a light-emitting portion provided on the window layer-cum-support substrate and including a second semiconductor layer of a second conductivity type, an active layer, and first semiconductor layer of a first conductivity type in stated order, a first ohmic electrode provided on the first semiconductor layer, and insulator top coat at least partially coating the first semiconductor layer surface and light-emitting portion side surface, wherein the first semiconductor layer surface and surface of the window layer-cum-support substrate are roughened, and the first semiconductor layer includes at least two layers of an active-layer-side layer and roughened-side layer, and roughened-side layer is formed of material having lower Al content than the active-layer-side layer. This light-emitting device can reduce etching depth required to obtain desired roughened shape and inhibit occurrence of chip cracks during wire bonding, while keeping effect of trapping carriers in the clad layer.

TECHNICAL FIELD

The present invention relates to a light-emitting device and a methodfor manufacturing a light-emitting device, and more particularly to astructure and a manufacturing method in which a first semiconductorlayer, an active layer, a second semiconductor layer, and a windowlayer-cum-support substrate are formed on a substrate by epitaxialgrowth, and after removing the substrate, the light-emitting devicesubstrate having electrodes formed thereon is subjected to surfaceroughening treatment.

BACKGROUND ART

In recent years, a light-emitting diode (LED) has improved itsefficiency and has been increasingly applied to lighting apparatuses.Most conventional lighting apparatuses combine an InGaN-based blue LEDand a fluorescent agent. Unfortunately, the use of the fluorescent agentinevitably causes stokes loss in principle, and not all lights receivedby the fluorescent agent can be converted into other wavelengths. Inparticular, this problem is prominent in regions of yellow and redhaving relatively longer wavelengths than that of blue.

To solve this problem, a technique combining a yellow or red LED with ablue LED has been recently adopted. In this regard, a bulb type lightingapparatus, in which LEDs are arranged on a board to form a filament foremitting light, has been widely spread rather than a COB (chip on board)type, in which light is extracted to one surface. LED devices used inthe apparatus of this type need to extract light over the entirefilament surface. Thus, a device that extracts light to one side is notsuitable, and a device having light distribution to extract light inevery direction of a chip is ideal.

For the InGaN-based LED, which is the blue LED, a sapphire substrate isgenerally used. The sapphire substrate is transparent to emissionwavelength, and thus is ideal for the above-described lightingapparatus. For the yellow or red LED, however, GaAs or Ge, which canabsorb light with emission wavelength, is used as a starting substrate,and is unsuitable for the above-described use.

To solve this problem, there have been disclosed a method in which atransparent substrate is bonded to a light-emitting portion as describedin Patent Document 1; and a technique in which a window layer is grownto have a sufficient thickness to be used as a support substrate, and astarting substrate that is a light-absorbing substrate is removed toprovide an LED as described in Patent Document 2.

The method disclosed in Patent Document 1 requires bonding a transparentsubstrate thicker than necessary, and grinding the substrate to apredetermined thickness after bonding, which can increase the cost.Moreover, the substrate used for bonding usually has a thickness of 200μm or more. Considering light distribution characteristics and assemblyproperties with other devices, the thickness required for an LED deviceis approximately 100 μm at most, and thus the substrate requiresthinning to this degree of thickness. The thinning processing increasesthe number of processes and a risk of cracking the wafer, causing anincrease in cost and a reduction in yield.

On the other hand, the method disclosed in Patent Document 2, whichutilizes, as a support substrate, a window layer grown by crystal growthto have a sufficient thickness for the support substrate, includesgrowing the window layer to a desired thickness, and does not requirethinning processing and substrate joining/bonding processes. Thus, thismethod enables low-cost formation and is excellent.

The light-emitting device having a transparent support substrate asdescribed above generally employs a technique for preventing multiplereflection within the light-emitting device and inhibiting lightabsorption in order to enhance luminous efficiency. Patent Document 3proposes a method for roughening the surfaces of a windowlayer-cum-current diffusion layer and a window layer-cum-supportsubstrate, but not roughening the surface of a light-emitting portion ina structure where the light-emitting portion is sandwiched between thethick window layer-cum-current diffusion layer and the thick windowlayer-cum-support substrate. However, this method requires forming adeep trench that pierces through the window layer-cum-current diffusionlayer, which increases the cost, and makes a vertical distance betweenupper and lower electrode portions large, which causes a difficulty inwire bonding. In the application to a flip chip type, a thick insulatorfilm and a very long metal via must be formed, which causes the increasein cost. It is thus desirable for the window layer-cum-current diffusionlayer used as the upper electrode portion to be thin.

Patent Documents 4 and 5 disclose techniques in which the windowlayer-cum-current diffusion layer is thin, the vertical distance betweenupper and lower electrode portions is short, and a light-extractingportion or a light-reflecting portion has a roughened surface. In PatentDocument 4, the roughened surface is formed on an n-type semiconductorlayer surface at the opposite side of a light-extracting surface.However, this disclosure relates to the flip chip type, and intends toefficiently reflect light from an electrode side to a window layer side.Moreover, this document discloses a difficulty in forming roughenedsurfaces on both the window layer-cum-support substrate and thelight-emitting portion.

Patent Document 5 discloses a technique for roughening the surface of anAlGaInP-based clad layer. According to the technique disclosed in PatentDocument 5, a clad layer is made of (Al_(0.5)Ga_(0.5))_(0.5)In_(0.5)P,and a window layer made of (Al_(x)Ga_(1-x))_(0.5)In_(0.5)P (0.5<x) isformed on an upper part of the clad layer. That is, the disclosedtechnique indicates that the layer to be roughened is made of a materialhaving a higher Al content than that of the clad layer.

CITATION LIST Patent Literature

Patent Document 1: Japanese Patent No. 5427585

Patent Document 2: Japanese Patent No. 4569858

Patent Document 3: Japanese Patent No. 4715370

Patent Document 4: Japanese Unexamined Patent Application PublicationNo. 2007-059518

Patent Document 5: Japanese Unexamined Patent Application Publication.No. 2010-251531

SUMMARY OF INVENTION Technical Problem

However, in the light-emitting device having the windowlayer-cum-support substrate portion and the light-emitting portion, ifan electrode with thin wire is provided on the surface of thelight-emitting portion, and the light-emitting portion is subjected tosurface roughening treatment by etching, a higher Al content leads to ahigher etching rate and makes the surface roughening treatmentdifficult. Thus, the etching depth requires increasing in order toobtain a desired roughened surface. As a result, excessive etching isperformed from the pad electrode forming surface, and the mechanicalstrength of the pad electrode portion is decreased. This increases arisk of causing cracks on a chip during wire bonding.

On the other hand, the Al content of the clad layer requires increasingin order to enhance an effect of trapping carriers that are implantedinto an active layer. However, as mentioned above, when the Al contentis increased, the etching depth is increased in order to obtain adesired roughened surface. Accordingly, it is also necessary tosignificantly increase the thickness of the clad layer to be thickerthan a minimum thickness required for trapping carriers.

Therefore, no one has yet disclosed a technique that can effectivelyperform the surface roughening treatment while keeping the effect oftrapping carriers in the clad layer and keeping the mechanical strengthof the bonding pad.

The present invention was accomplished in view of the above-describedproblems. It is an object of the present invention to provide alight-emitting device that has a window layer-cum-support substrate anda light-emitting portion, and can reduce the etching depth required toobtain a desired roughened shape and inhibit occurrence of chip cracksduring wire bonding, while keeping the effect of trapping carriers inthe clad layer, when the surface of the light-emitting portion isroughened by a surface roughening liquid (an etching liquid).

Solution to Problem

To achieve this object, the present invention provides a light-emittingdevice comprising: a window layer-cum-support substrate; and alight-emitting portion provided on the window layer-cum-supportsubstrate and including a second semiconductor layer of a secondconductivity type, an active layer, and a first semiconductor layer of afirst conductivity type in the stated order, the light-emitting devicefurther comprising:

a first ohmic electrode provided on the first semiconductor layer; andan insulator top coat at least partially coating a surface of the firstsemiconductor layer and a side surface of the light-emitting portion,wherein

the surface of the first semiconductor layer and a surface of the windowlayer-cum-support substrate are roughened, and

the first semiconductor layer includes at least two layers of anactive-layer-side layer and a roughened-side layer, and theroughened-side layer is formed of a material having a lower Al contentthan that of the active-layer-side layer.

This light-emitting device can reduce the etching depth required toobtain a desired roughened shape and inhibit occurrence of chip cracksduring wire bonding, while keeping the effect of trapping carriers inthe clad layer.

The light-emitting device preferably comprises a removal section inwhich a part of the light-emitting portion is removed; a non-removalsection other than the removal section; the first ohmic electrodeprovided on the first semiconductor layer in the non-removal section;and a second ohmic electrode provided on the window layer-cum-supportsubstrate or the second semiconductor layer in the removal section.

Such a structure makes the present invention more effective.

Preferably, the roughened-side layer of the first semiconductor layercomprises (Al_(x)Ga_(1-x))_(y)In_(1-y)P where 0≤x<0.6 and 0.4≤y≤0.6, orAl_(z)Ga_(1-z)As where 0≤z≤0.3, and

the active-layer-side layer of the first semiconductor layer comprises(Al_(x)Ga_(1-x))_(y)In_(1-y)P where 0.6≤x≤1 and 0.4≤y≤0.6, orAl_(z)Ga_(1-z)As where 0.3<z≤1.

This ensures that the light-emitting device can reduce the etching depthrequired to obtain a desired roughened shape and inhibit occurrence ofchip cracks during wire bonding, while keeping the effect of trappingcarriers in the clad layer.

Furthermore, the present invention provides a method for manufacturing alight-emitting device, the method comprising:

a step of forming a light-emitting portion by sequentially growing afirst semiconductor layer, an active layer, and a second semiconductorlayer on a substrate by epitaxial growth using a material whose latticematches with the substrate;

a step of forming a window layer-cum-support substrate on thelight-emitting portion by epitaxial growth using a material whoselattice mismatches with the substrate; a step of removing the substrate;

a step of forming a first ohmic electrode on the first semiconductorlayer;

a first surface roughening treatment step of roughening a surface of thefirst semiconductor layer;

a device isolation step of forming a removal section in which a part ofthe light-emitting portion is removed and a non-removal section otherthan the removal section;

a step of forming a second ohmic electrode on the windowlayer-cum-support substrate with the light-emitting portion beingremoved therefrom;

a step of at least partially coating the surface of the firstsemiconductor layer and a side surface of the light-emitting portionwith an insulator top coat; and

a second surface roughening treatment step of roughening a surface and aside surface of the window layer-cum-support substrate, wherein

in the step of forming the light-emitting portion, the firstsemiconductor layer is formed so as to have at least two layers of anactive-layer-side layer and a roughened-side layer, and theroughened-side layer is formed of a material having a lower Al contentthan that of the active-layer-side layer.

This manufacturing method enables manufacture of a light-emitting devicethat can reduce the etching depth required to obtain a desired roughenedshape and inhibit occurrence of chip cracks during wire bonding, whilekeeping the effect of trapping carriers in the clad layer.

Preferably, the roughened-side layer of the first semiconductor layercomprises (Al_(x)Ga_(1-x))_(y)In_(1-y)P where 0≤x<0.6 and 0.4≤y≤0.6, orAl_(z)Ga_(1-z)As where 0≤z≤0.3, and

the active-layer-side layer of the first semiconductor layer comprises(Al_(x)Ga_(1-x))_(y)In_(1-y)P where 0.6≤x≤1 and 0.4≤y≤0.6, orAl_(z)Ga_(1-z)As where 0.3<z≤1.

This ensures manufacture of a light-emitting device that can reduce theetching depth required to obtain a desired roughened shape and inhibitoccurrence of chip cracks during wire bonding, while keeping the effectof trapping carriers in the clad layer.

Preferably, the first surface roughening treatment step is carried outby using a liquid mixture of an organic acid and an inorganic acid, theorganic acid including any one or more of citric acid, malonic acid,formic acid, acetic acid, and tartaric acid, the inorganic acidincluding any one or more of hydrochloric acid, sulfuric acid, nitricacid, and hydrofluoric acid, and

the second surface roughening treatment step is carried out by using amixed solution containing iodine, an organic acid, and an inorganicacid, the organic acid including any one or more of citric acid, malonicacid, formic acid, acetic acid, and tartaric acid, the inorganic acidincluding any one or more of hydrochloric acid, sulfuric acid, nitricacid, and hydrofluoric acid.

In this manner, a light-emitting device having a roughened surface witha desired size of irregularities can be surely manufactured.

Advantageous Effects of Invention

The present invention can provide a light-emitting device that canreduce the etching depth required to obtain a desired roughened shapeand inhibit occurrence of chip cracks during wire bonding, while keepingthe effect of trapping carriers in the clad layer.

Furthermore, the method for manufacturing a light-emitting deviceaccording to the present invention enables manufacture of alight-emitting device that can reduce the etching depth required toobtain a desired roughened shape and inhibit occurrence of chip cracksduring wire bonding, while keeping the effect of trapping carriers inthe clad layer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing an example of the light-emittingdevice according to the present invention;

FIG. 2 is a process drawing showing an example of the method formanufacturing a light-emitting device according to the presentinvention;

FIG. 3 is a schematic view showing an epitaxial substrate having aselective etching layer, a light-emitting portion, and a windowlayer-cum-support substrate grown on a substrate in a manufacturingprocess of the method for manufacturing a light-emitting deviceaccording to the present invention;

FIG. 4 is a schematic view showing a light-emitting device substrateprovided by removing the substrate and a second selective etching layerfrom the epitaxial substrate in the manufacturing process of the methodfor manufacturing a light-emitting device according to the presentinvention;

FIG. 5 is a schematic view showing the light-emitting device substratehaving a first ohmic electrode formed thereon in the manufacturingprocess of the method for manufacturing a light-emitting deviceaccording to the present invention;

FIG. 6 is a schematic view showing the light-emitting device substratesubjected to the first surface roughening treatment in the manufacturingprocess of the method for manufacturing a light-emitting deviceaccording to the present invention;

FIG. 7 is a schematic view showing the light-emitting device substratesubjected to the device isolation step in the manufacturing process ofthe method for manufacturing a light-emitting device according to thepresent invention; and

FIG. 8 is a schematic view showing the light-emitting device substratehaving a second ohmic electrode and an insulator top coat formed thereonin the manufacturing process of the method for manufacturing alight-emitting device according to the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described, butthe present invention is not limited thereto.

As mentioned above, the following problem arises in recent years: in alight-emitting portion having a roughened surface formed by a surfaceroughening liquid, if a layer with the roughened surface has an Alcontent equal to or higher than that of a clad layer part, irregularitysize on the roughened surface is reduced due to an excessively highetching rate, and the surface roughening treatment cannot be effectivelyperformed. In view of this, the present inventors repeatedly and keenlyconducted studies to prevent the high etching rate at surface rougheningetching and following insufficient irregularity.

As a result, they found that when the first semiconductor layer iscomposed of two or more layers each having Al composition, in which amaterial of the layer to be roughened has a lower Al content than thatof the layer at the active layer side, it is possible to prevent theoccurrence of chip cracks during wire bonding by the reduction inmechanical strength of the pad electrode portion due to excessiveetching, while keeping the effect of trapping carriers in the cladlayer, and thus a roughened surface with desired irregularities can beobtained. Then, they considered the best embodiment to realize the aboveideas, thereby bringing the present invention to completion.

First, the light-emitting device according to the present invention willbe described with reference to FIG. 1.

As shown in FIG. 1, a light-emitting device 1 of the present inventionhas a window layer-cum-support substrate 107 and a light-emittingportion 108 that is provided on the window layer-cum-support substrate107 and includes a second semiconductor layer 105 of a secondconductivity type, an active layer 104, and a first semiconductor layer103 of a first conductivity type in the stated order.

On the first semiconductor layer 103, a first ohmic electrode 121 isprovided. Additionally, a surface of the first semiconductor layer 103and a side surface of the light-emitting portion 108 are at leastpartially coated with an insulator top coat 150, and the surface of thefirst semiconductor layer 103 and a surface and a side surface of thewindow layer-cum-support substrate 107 are roughened.

As shown in FIG. 1, the first ohmic electrode 121 may be provided on thefirst semiconductor layer 103 with a first selective etching layer 102Bbeing inserted therebetween.

As shown in FIG. 1, the first semiconductor layer 103 includes at leasttwo layers. The roughened-side layer (hereinafter, referred to as alow-Al-content layer 103A) is formed of a material having a lower Alcontent than that of the active-layer-side layer (hereinafter, referredto as a high-Al-content layer 103B).

More specifically, the low-Al-content layer 103A may be composed of(Al_(x)Ga_(1-x))_(y)In_(1-y)P (0≤x<0.6, 0.4≤y≤0.6) or Al_(z)Ga_(1-z)As(0≤z≤0.3), while the high-Al-content layer 103B may be composed of(Al_(x)Ga_(1-x))_(y)In_(1-y)P (0.6≤x≤1, 0.4≤y≤0.6) or Al_(z)Ga_(1-z)As(0.3<z≤1).

The light-emitting device 1 preferably includes a removal section 170 inwhich at least the first semiconductor layer 103 and the active layer104 of the light-emitting portion 108 are removed, and a non-removalsection 180 other than the removal section 170. When the light-emittingportion is removed up to the active layer 104, the surface of theremoval section 170 is the second semiconductor layer 105. When thelight-emitting portion is removed up to a buffer layer 106, the surfaceof the removal section 170 is the window layer-cum-support substrate107.

Furthermore, the light-emitting device preferably includes the firstohmic electrode 121 provided on the first semiconductor layer 103 in thenon-removal section 180 and a second ohmic electrode 122 provided on thewindow layer-cum-support substrate 107 or the second semiconductor layer105 in the removal section 170.

Such a structure makes the present invention more effective.

Such a light-emitting device of the present invention can reduce theetching depth required to obtain a desired roughened shape and inhibitoccurrence of chip cracks during wire bonding, while keeping the effectof trapping carriers in the clad layer.

Next, the method for manufacturing a light-emitting device according tothe present invention will be described with reference to FIG. 2 to FIG.8.

First, as shown in FIG. 3, a substrate 101 is prepared as a startingsubstrate (SP1 in FIG. 2).

As the substrate 101, GaAs or Ge can be preferably used.

This allows epitaxial growth using a lattice-matched material to form anactive layer 104 described later, and thus can easily improve quality ofthe active layer 104, improving luminance and lifetime characteristics.

Then, a selective etching layer 102 may be formed on the substrate 101(SP2 in FIG. 2).

The selective etching layer 102 can be formed on the substrate 101 by,for example, an MOVPE method (a metal organic vapor phase epitaxymethod), MBE (molecular beam epitaxy method), or CBE (chemical beamepitaxy method).

The selective etching layer 102 is preferably formed of two or morelayers, including at least a second selective etching layer 102Aadjoining the substrate 101 and a first selective etching layer 102Badjoining a later-described first semiconductor layer 103. Materials orcompositions of the second selective etching layer 102A and the firstselective etching layer 102B may be different from each other.

Then, a first semiconductor layer 103 of a first conductivity type, anactive layer 104, and a second semiconductor layer 105 of a secondconductivity type that have lattice matching with the substrate 101 aresequentially grown by epitaxial growth to form a light-emitting portion108 (SP3 in FIG. 2).

Then, a window layer-cum-support substrate 107 is formed on thelight-emitting portion 108 by epitaxial growth using a material whoselattice mismatches with the substrate 101 to produce an epitaxialsubstrate 109 (SP4 in FIG. 2).

In SP3 and 4, specifically, as shown in FIG. 3, a buffer layer 106 andthe window layer-cum-support substrate 107 may be formed by epitaxialgrowth, in the stated order, on the light-emitting portion 108 composedof the first semiconductor layer 103 of a first conductivity type, theactive layer 104, and the second semiconductor layer 105 of a secondconductivity type to produce the epitaxial substrate 109.

The window layer-cum-support substrate 107 may be formed by an HVPEmethod (a hydride vapor phase epitaxy method).

The active layer 104 may be formed of (Al_(x)Ga_(1-x))_(y)In_(1-y)P(0≤x≤1, 0.4≤y≤0.6) or Al_(z)Ga_(1-z)As (0≤z≤0.45), depending on emissionwavelength. For example, AlGaInP is preferably selected for theapplication to visible light illumination, and AlGaAs is preferablyselected for the application to infrared illumination. However, asregards the design of the active layer 104, since the wavelength can beadjusted to be a wavelength other than that attributable to the materialcomposition by use of superlattice or the like, this layer is notrestricted to the above materials.

AlGaInP or AlGaAs is selected for the first semiconductor layer 103 andthe second semiconductor layer 105, and this selection is notnecessarily the same as the material of the active layer 104.

The present embodiment shows the case where the structure is the mostsimplest, i.e., the first semiconductor layer 103, the active layer 104,and the second semiconductor layer 105 are made of the same material,AlGaInP. However, each layer of the first semiconductor layer 103 andthe second semiconductor layer 105 usually contains a plurality oflayers to improve characteristics, and each of the first semiconductorlayer 103 and the second semiconductor layer 105 is not limited to asingle layer, needless to say.

The first semiconductor layer 103 is formed so as to have at least twolayers. In the first semiconductor layer 103, the low-Al-content layer103A at the side to be roughened is formed of a material having a lowerAl content than that of the high-Al-content layer 103B at the activelayer side.

The high-Al-content layer 103B is a functional layer that functions as aclad layer, and is not limited to a single composition or a singlecondition layer.

More specifically, the low-Al-content layer 103A may be composed of(Al_(x)Ga_(1-x))_(y)In_(1-y)P (0≤x<0.6, 0.4≤y≤0.6) or Al_(z)Ga_(1-z)As(0≤z≤0.3), while the high-Al-content layer 103B may be composed of(Al_(x)Ga_(1-x))_(y)In_(1-y)P (0.6≤x≤1, 0.4≤y≤0.6) or Al_(z)Ga_(1-z)As(0.3<z≤1).

For the window layer-cum-support substrate 107, GaP, GaAsP, AlGaAs,sapphire (Al₂O₃), quartz (SiO₂), SiC, or the like can be preferablyused. When the window layer-cum-support substrate 107 is formed of GaAsPor GaP, the buffer layer 106 is most preferably formed of GaInP.However, a material of the buffer layer 106 may be any material that hasa buffering function, and is not limited to the above material, needlessto say.

Moreover, when GaAsP is selected for the window layer-cum-supportsubstrate 107, weather resistance is excellent.

However, since GaAsP has considerable lattice mismatch with anAlGaInP-based material or an AlGaAs-based material, GaAsP is givenhigh-density distortion or threading dislocation. Consequently, theepitaxial substrate 109 has large warp.

To avoid a wavelength shift due to formation of natural superlattice,the light-emitting section 108 is preferably grown with acrystallographic inclination at 12 degrees or more to a growth surface.Although any direction can be selected as the inclining direction, whena scribing and breaking process is employed in the device isolationstep, one scribe line may be selected in a direction in which a crystalaxis is orthogonal without inclination, while the other scribe line maybe selected in a direction in which the crystal axis is inclined. Thisenables a reduction of a plane where the side surface of the deviceinclines to the front surface and the back surface of the device. Thus,a non-inclined direction is usually selected for the one scribe line.However, about 20 degrees of inclination of the device side surface isnot a serious problem in assembly. Therefore, the orthogonal directiondoes not have to be accurately orthogonal, and permits an angular rangeof about ±20 degrees from a right angle.

Then, the substrate 101 and the second selective etching layer 102A areremoved from the epitaxial substrate 109, and only the first selectiveetching layer 102B is left on the surface of the first semiconductorlayer 103 to form a light-emitting device substrate 110, as shown inFIG. 4 (SP5 in FIG. 2).

More specifically, only the first selective etching layer 102B can beleft on the surface of the first semiconductor layer 103 by removing thesubstrate 101 from the epitaxial substrate 109 according to a wetetching method using the second selective etching layer 102A.

Then, as shown in FIG. 5, a first ohmic electrode 121 for supplying apotential to the light-emitting device is formed on the surface of thefirst selective etching layer 102B on the first semiconductor layer 103(SP6 in FIG. 2).

Then, as shown in FIG. 5, a region of the first selective etching layer102B other than a part under the first ohmic electrode 121 is removed(SP7 in FIG. 2).

More specifically, the region of the first selective etching layer 102Bother than the part under the first ohmic electrode 121 can be removedby etching using the first ohmic electrode 121 as an etching mask.

Then, as shown in FIG. 6, the surface of the first semiconductor layer103 is roughened in a first surface roughening treatment step (SP8 inFIG. 2).

The first surface roughening treatment step may be carried out by usinga liquid mixture of an organic acid and an inorganic acid, in which theorganic acid may include a carboxylic acid, particularly, any one ormore of citric acid, malonic acid, formic acid, acetic acid, andtartaric acid, and the inorganic acid may include one or more ofhydrochloric acid, sulfuric acid, nitric acid, and hydrofluoric acid.

In this manner, the surface can be surely roughened.

At this time, the first surface roughening liquid is preferably used formainly subjecting the low-Al-content layer 103A to the first surfaceroughening treatment. In the case that the low-Al-content layer 103A andthe high-Al-content layer 103B are made of the same type of materials,for example, both the layers are made of AlGaInP-based materials, theetching rate of the high-Al-content layer 103B is higher than that ofthe low-Al-content layer 103A. Thus, if etching of the high-Al-contentlayer 103B is undesirable, the thickness of the low-Al-content layer103A is preferably made thicker than a depth to be etched.

On the other hand, if one intends to partially etch the high-Al-contentlayer 103B by using irregularities generated on the low-Al-content layer103A as an etching pattern to increase the irregularities, the thicknessof the low-Al-content layer 103A is preferably made thinner than a depthto be etched.

In the first surface roughening treatment step, the size ofirregularities on the roughened surface can be determined by an Alcontent of the low-Al-content layer 103A. For example, a roughness R_(a)(arithmetic average roughness) of about 0.3 μm can be achieved byetching the low-Al-content layer 103A having the above composition withan etching depth of, e.g., 0.3 to 0.6 μm.

On the other hand, when the etching depth is decreased to less than 0.3to 0.6 μm, R_(a) can be reduced. Moreover, when the etching depth isincreased to more than 0.3 to 0.6 μm, R_(a) can be reduced since theroughened surface is flattened.

For increasing R_(a), the low-Al-content layer 103A is formed to beslightly thinner than a depth to be etched. Since the low-Al-contentlayer has low etching rate whereas the high-Al-content layer has highetching rate the etching rate is accelerated from a part where thelow-Al-content layer 103A is removed by etching. The part is deeplyetched, and R_(a) is increased.

In addition, when the first selective etching layer 102B is made of amaterial having an etching selectivity to the first surface rougheningliquid, the first surface roughening liquid forms a facet plane alongthe shape of the first ohmic electrode. In this manner, providing thefirst selective etching layer 102B under the first ohmic electrode 121prevents occurrence of over-etching under the first ohmic electrode 121,inhibiting separation of the electrode on the surface of thelight-emitting portion.

Then, as shown in FIG. 7, a part of the light-emitting portion 108 isremoved to form a removal section 170 and a non-removal section 180other than the removal section in a device isolation step (SP9 in FIG.2).

The device isolation step can be carried out by, for example, forming apattern of a resist in which predetermined regions (a second ohmicelectrode forming region 140 and a scribe region 141 in FIG. 6) on thefirst semiconductor layer 103 are opened, according to aphotolithography method, and performing etching using the resist as anetching mask.

The etching enables formation of the removal section 170 in which thesecond semiconductor layer 105, the buffer layer 106, or the windowlayer-cum support substrate 107 are exposed, and the non-removal section180 other than the removal section 170, according to a wet etchingmethod using a wet etchant containing hydrochloric acid.

Alternatively, the device isolation may be carried out by a dry etchingmethod such as an RIE method or an ICP method using a halogen gas,preferably a gas containing hydrogen chloride, besides the wet etchingmethod described above.

Then, as shown in FIG. 8, a second ohmic electrode 122 is formed, in theremoval section 170, on the window layer-cum-support substrate 107 orthe second semiconductor layer 105 from which the light-emitting portion108 has been removed (SP10 in FIG. 2).

Then, as shown in FIG. 8, the surface of the first semiconductor layer103 and the side surface of the light-emitting portion 108 are at leastpartially coated with an insulator top coat 150 (SP11 in FIG. 2).

The insulator top coat 150 may be made of any material that hastransparency and insulating property. As the insulator top coat 150, forexample, SiO₂ or SiN_(x) is preferably used. Such materials facilitateprocessing for opening an upper part of the first ohmic electrode 121 bythe photolithography method with an etching liquid containinghydrofluoric acid.

Then, as shown in FIG. 1, the surface and the side surface of the windowlayer-cum-support substrate 107 are roughened in a second surfaceroughening treatment step (SP12 in FIG. 2).

Prior to the second surface roughening treatment, a light-emittingdevice dice is preferably formed by drawing scribe lines along theremoval section 170 and breaking and isolating the light-emittingdevice. After forming the light-emitting device dice, the light-emittingdevice dice is preferably transferred to a holding tape with the windowlayer-cum-support substrate 107 upside before the second surfaceroughening treatment.

The second surface roughening treatment step may be carried out by usinga mixed solution containing iodine, an organic acid, and an inorganicacid, in which the organic acid may include any one or more of citricacid, malonic acid, formic acid, acetic acid, and tartaric acid, and theinorganic acid may include any one or more of hydrochloric acid,sulfuric acid, nitric acid, and hydrofluoric acid.

In this manner, the surface can be surely roughened.

The second surface roughening liquid used for roughening the windowlayer-cum-support substrate 107 in the second surface rougheningtreatment step has different liquid composition from that of theabove-described first surface roughening liquid used for roughening thefirst semiconductor layer 103 in the first surface roughening treatmentstep. Thus, these liquids have different etching properties, which leadto different shapes and R_(a) of the roughened surfaces of the firstsemiconductor layer 103 and the window layer-cum-support substrate 107.

The above-described method enables prevention of the occurrence of chipcracks during wire bonding by the reduction in mechanical strength ofthe pad electrode portion due to excessive etching, while keeping theeffect of trapping carriers in the clad layer, whereby a light-emittingdevice having a roughened surface with desired irregularity size can bemanufactured.

Example

Hereinafter, the present invention will be more specifically describedwith reference to Example and Comparative example, but the presentinvention is not limited thereto.

Example

0.5 μm of an n-type GaAs buffer layer (not shown), 1 μm of a secondselective etching layer 102A made of an n-type AlInP layer, and 1 μm ofa first selective etching layer 102B made of an n-type GaAs layer weregrown on an n-type GaAs substrate 101 with a thickness of 280 μm havinga crystal axis inclined at 15° toward a [110] direction from a [001]direction. Then, 5.5 μm of a light-emitting portion 108 constituted ofan n-type clad layer (a first semiconductor layer 103), an active layer104, and a p-type clad layer (a second semiconductor layer 105) whichwere made of AlGaInP was formed by the MOVPE method. Further, 0.3 μm ofa buffer layer 106 made of p-type GaInP was formed, and 1 μm of a layermade of p-type GaP was formed as a part of a GaP windowlayer-cum-support substrate 107. Then, the product was put into an HVPEfurnace, and 120 μm of the window layer-cum-support substrate 107 madeof p-type GaP was grown to obtain an epitaxial substrate 109 (see FIG.3).

The active layer 104 was formed of a plurality of layers made ofAlGaInP.

The first semiconductor layer was formed of two layers of alow-Al-content layer 103A and a high-Al-content layer 103B.

The high-Al-content layer 103B had a thickness of 2.0 μm and contained aplurality of layers made of (Al_(x)Ga_(1-x))_(0.5)In_(0.5)P (0.70≤x≤1).The low-Al-content layer 103A had a thickness of 0.6 μm and was made of(Al_(0.4)Ga_(0.6))_(0.5)In_(0.5)P.

The second semiconductor layer 105 had a thickness of 1.5 μm andcontained a plurality of layers made of (Al_(x)Ga_(1-x))_(0.5)In_(0.5)P(0.3≤x≤1).

Then, the substrate 101, the GaAs buffer layer, and the second selectiveetching layer 102A were removed by etching to produce a light-emittingdevice substrate 110 in which the first selective etching layer 102Bremained (see FIG. 4).

Then, a first ohmic electrode 121 was formed on the first selectiveetching layer 102B of the light-emitting device substrate 110 (see FIG.5), and the first selective etching layer 102B was selectively removedby SPM treatment using the first ohmic electrode 121 as a mask.

Then, the surface of the low-Al-content layer 103A, which was placed inthe outermost of the first semiconductor layer 103, was subjected to thefirst surface roughening treatment step (see FIG. 6). A liquid mixtureof acetic acid and hydrochloric acid was prepared as the first surfaceroughening liquid and used in etching at room temperature for 1 minuteto perform the surface roughening treatment. Roughness R_(a) of theroughened surface of the first semiconductor layer 103 at this time wasmeasured.

In addition, maximum, minimum, and average values of the etching depthat this time were also measured. In the measurement, the shallowestpoint of irregularities formed by the first surface roughening treatmentwas defined as the minimum value of the etching depth; the deepest pointwas defined as the maximum value; and a nearly mean point between theshallowest point and the deepest point was defined as the average value.

Table 1 shows the results measured as above. Table 1 also shows resultsof Comparative example described later.

TABLE 1 Maxinium Minimum Average value value value of etching of etchingof etching Ra depth [μm] depth [μm] depth [μm] [μm] Example 0.54 0.110.41 0.32 Comparative 1.17 0.71 0.92 0.33 example

As shown in Table 1, in Example, R_(a) was 0.32 μm. The maximum value ofthe etching depth was 0.54 μm, the minimum value was 0.11 μm, and theaverage value was 0.41 μm. On the other hand, in Comparative exampledescribed later, R_(a) was 0.33 μm, which was almost equal to the valuein Example, but 0.92 μm of the average etching depth was required in thefirst surface roughening treatment to achieve this roughness.

Thus, Examples could reduce the etching depth required to obtain adesired roughened shape, compared with Comparative example describedlater.

Then, regions other than a second ohmic electrode forming region 140 anda scribe region 141 (see FIG. 6) were covered with a resist by thephotolithography method, the device isolation step was carried out bythe wet etching method with a wet etchant containing hydrochloric acid,and the light-emitting section 108 was removed to form a removal section170 in which the window layer-cum-support substrate 107 was exposed anda non-removal section 180 other than the removal section 170 (see FIG.7).

Then, a second ohmic electrode 122 was formed in the removal section 170(see FIG. 8). Subsequently, an insulator top coat 150 made of SiO₂ waslaminated to cover the surface of the first semiconductor layer 103 andthe side surface of the light-emitting section 108 with the insulatortop coat 150. Furthermore, openings were formed in the insulator topcoat 150 by processing portions of the first ohmic electrode 121 by thephotolithography method and hydrofluoric acid etching.

Then, scribe lines were drawn along the removal section 170, and cracklines were extended along the scribe lines. Thereafter, breaking wascarried out to isolate the device, whereby a light-emitting device dicewas formed.

After forming the light-emitting device dice, the light-emitting devicedice was transferred to a holding tape such that the surface having thefirst ohmic electrode faced the tape side. Thereafter, the secondsurface roughening treatment step was carried out. A surface rougheningliquid used for roughening the surface of the window layer-cum-supportsubstrate in the second surface roughening treatment step was preparedby mixing acetic acid, hydrofluoric acid, and iodine. Then, the secondsurface roughening treatment was carried out by etching at roomtemperature for 1 minute. When roughness of the roughened surface wasmeasured on the surface and the side surface of the windowlayer-cum-support substrate 107, R_(a) was 0.5 μm.

Thus, a light-emitting device in which the etching depth required toobtain a desired roughened shape was reduced while keeping the effect oftrapping carriers in the clad layer could be manufactured.

Furthermore, an LED chip was manufactured by wire bonding.

As a result, the LED chip could be manufactured without causing chipcracks during wire bonding.

Comparative Example

A light-emitting device was manufactured in the same procedure as inExample except that no low-Al-content layer, but an n-type clad layerwith the same thickness as in Example was formed as the layer to besubjected to the first surface roughening treatment.

Thereafter, an LED chip was manufactured by wire bonding as in Example.

The surface roughness after the first surface roughening treatment wasmeasured as in Example. The measurement result is shown in Table 1.

As shown in Table 1, roughness R_(a) after the first surface rougheningtreatment was 0.33. The maximum value of the etching depth required toachieve this roughness in the first surface roughening treatment was1.17 μm; the minimum value was 0.71 μm; and the average value was 0.92μm.

Moreover, when the roughness after the second surface rougheningtreatment was measured as in Example, R_(a) was 0.5 μm.

Moreover, in Comparative example, shock absorbing ability at wirebonding was lowered, and chip cracks were caused.

It is to be noted that the present invention is not limited to theforegoing embodiment. The embodiment is just an exemplification, and anyexamples that have substantially the same feature and demonstrate thesame functions and effects as those in the technical concept describedin claims of the present invention are included in the technical scopeof the present invention.

The invention claimed is:
 1. A light-emitting device comprising: awindow layer-cum-support substrate; a light-emitting portion provided onthe window layer-cum-support substrate and including a secondsemiconductor layer of a second conductivity type, an active layer, anda first semiconductor layer of a first conductivity type in the statedorder; a first ohmic electrode provided on the first semiconductorlayer; and an insulator top coat at least partially coating a surface ofthe first semiconductor layer and a side surface of the light-emittingportion, wherein the surface of the first semiconductor layer and asurface of the window layer-cum-support substrate are roughened, thefirst semiconductor layer includes at least two layers of anactive-layer-side layer and a roughened-side layer, and theroughened-side layer is formed of a material having a lower Al contentthan that of the active-layer-side layer, and the roughened-side layerof the first semiconductor layer comprises (Al_(x)Ga_(1-x))_(y)In_(1-y)Pwhere 0≤x<0.6 and 0.4≤y≤0.6, or Al_(z)Ga_(1-z)As where 0≤z≤0.3, and theactive-layer-side layer of the first semiconductor layer comprises(Al_(x)Ga_(1-x))_(y)In_(1-y)P where 0.6≤x≤1 and 0.4≤y≤0.6, orAl_(z)Ga_(1-z)As where 0.3<z≤1.
 2. The light-emitting device accordingto claim 1, wherein the light-emitting device further comprises: aremoval section in which a part of the light-emitting portion isremoved; a non-removal section other than the removal section, the firstohmic electrode provided on the first semiconductor layer in thenon-removal section; and a second ohmic electrode provided on the windowlayer-cum-support substrate or the second semiconductor layer in theremoval section.
 3. A method for manufacturing a light-emitting device,the method comprising: a step of forming a light-emitting portion bysequentially growing a first semiconductor layer, an active layer, and asecond semiconductor layer in this order on a substrate by epitaxialgrowth using a material whose lattice matches with the substrate; a stepof forming a window layer-cum-support substrate on the light-emittingportion by epitaxial growth using a material whose lattice mismatcheswith the substrate; a step of removing the substrate after the step offorming the window layer-cum-support substrate; a step of forming afirst ohmic electrode on the first semiconductor layer; a first surfaceroughening treatment step of roughening a surface of the firstsemiconductor layer; a device isolation step of forming a removalsection in which a part of the light-emitting portion is removed and anon-removal section other than the removal section; a step of forming asecond ohmic electrode on the window layer-cum-support substrate withthe light-emitting portion being removed therefrom; a step of at leastpartially coating the surface of the first semiconductor layer and aside surface of the light-emitting portion with an insulator top coat;and a second surface roughening treatment step of roughening a surfaceand a side surface of the window layer-cum-support substrate, wherein inthe step of forming the light-emitting portion, the first semiconductorlayer is formed so as to have at least two layers of anactive-layer-side layer and a roughened-side layer, and theroughened-side layer is formed of a material having a lower Al contentthan that of the active-layer-side layer.
 4. The method formanufacturing a light-emitting device according to claim 3, wherein theroughened-side layer of the first semiconductor layer comprises(Al_(x)Ga_(1-x))_(y)In_(1-y)P where 0≤x<0.6 and 0.4≤y≤0.6, orAl_(z)Ga_(1-z)As where 0≤z≤0.3, and the active-layer-side layer of thefirst semiconductor layer comprises (Al_(x)Ga_(1-x))_(y)In_(1-y)P where0.6≤x≤1 and 0.4≤y≤0.6, or Al_(z)Ga_(1-z)As where 0.3<z≤1.
 5. The methodfor manufacturing a light-emitting device according to claim 3, whereinthe first surface roughening treatment step is carried out by using aliquid mixture of an organic acid and an inorganic acid, the organicacid including any one or more of citric acid, malonic acid, formicacid, acetic acid, and tartaric acid, the inorganic acid including anyone or more of hydrochloric acid, sulfuric acid, nitric acid, andhydrofluoric acid, and the second surface roughening treatment step iscarried out by using a mixed solution containing iodine, an organicacid, and an inorganic acid, the organic acid including any one or moreof citric acid, malonic acid, formic acid, acetic acid, and tartaricacid, the inorganic acid including any one or more of hydrochloric acid,sulfuric acid, nitric acid, and hydrofluoric acid.
 6. The method formanufacturing a light-emitting device according to claim 4, wherein thefirst surface roughening treatment step is carried out by using a liquidmixture of an organic acid and an inorganic acid, the organic acidincluding any one or more of citric acid, malonic acid, formic acid,acetic acid, and tartaric acid, the inorganic acid including any one ormore of hydrochloric acid, sulfuric acid, nitric acid, and hydrofluoricacid, and the second surface roughening treatment step is carried out byusing a mixed solution containing iodine, an organic acid, and aninorganic acid, the organic acid including any one or more of citricacid, malonic acid, formic acid, acetic acid, and tartaric acid, theinorganic acid including any one or more of hydrochloric acid, sulfuricacid, nitric acid, and hydrofluoric acid.